Deflection circuit



Filed March 24, 1943 INVENTOR SYM/050% www ATTO R N EY Patented June 21, 1949 oraal-ce 'DEFLEC'IION CIRCUKT f' Application-March" 24, 1943', Serial'No; 480,360 ELIn the Netherlands Aprill' 3;"1941 Section 1.-PublicLaw 690, August 8, 1946 Patent expires April. 3,.1961

ft-Claims. g 1'.

'In 4circuit arrangements" for' supplying a. sawtootheshape'd current'to the'` deecting coils Aof a v.cathode-ray.tube, these .coils are' interposed in the anode` circuit off ,an .amplifying tube, -whose control ,grid hasisuppliedto' 'it a sawtooth-shaped voltage. .In..-.or.derf.topreventjthe direct .anode current .rorniiowing4 through .the Ideiiecting coils,. v/hich-wouldinvolvev an. undesirable deviation,.or,..d'lection...f.theiluminous spot on the screen. .of I .the zca.thode=1'ay. .,t'ub'e'; the anode -voltagei'smsuaHy.. supplied.to.;the. anode. of' the tube through acirouit connect'edein parallel. with'the defiecting coils. However,...the-.,provision of l the parallelcircuit-.involves distortion of'the sawtooth-shaped current through the deflecting coils. In fact, if thecircuit issuch-tiratil the total anode current is sawtooth-shaped when a sawtooth voltage is applied tofthe"grid^ofthetube, which is the case when lmaking use-of-a tube having a high internalz'resistance; thea-current through the deecting coils will generally no longer be sawtootheshaped, because vvthe current through the; parallel v"circuit is' subtracted "from thel total anode --current. -'Girly *whenthe""ratio L/R "of the: parallel 'circuit"correspondsf'ito that of v'the deecting"coi1sorwhen/ the inductance inserted in 1r the fparallel "circuit is" veryhi'gh with' respect to-"thefirrductance `of the"'de1ieeting coils,- the current v4'through the "deflectingvcoil would fremain sawtootheshape'd.

(However, upon `reducing to; -practice i'each of the two aboveementioned" conditions difficulties are experienced. If, for instance, the parallel circuit is composed in such manner that the ratio L/R thereof corresponds to that of the load circuit, the efficiency of the circuit becomes very bad. In addition, the available grid space of the tube becomes small due to the comparatively high ohmic resistance included in the anodesupply circuit. This may be explained by giving a practical example.

In a cathode-ray tube with magnetic deflection use was made of coils having an inductance of 1.7 henry and an ohmic resistance of 2800 ohms, which coils were fed from an amplifying tube whose average anode current amounted to '70 milliamperes at an anode voltage of 250 volts. If parallel feeding were used in such manner that the inductance and the ohmic resistance in the parallel circuit are equal to those of the deflecting -2 coils, in which case consequently an efficiency loss of 50% will already occur, then an average voltage loss of 0.07 2800=196'volts would occur in the supply circ-uit.

'Even when' the -inductancein ythe feedx circuit.` is given a hig-hvalue withtrespect to that-ofthe d'eiiectingcoil the results-'gare not satisfactory. Infact, if it is-'desired that the parallel-icircuit should havey al negligiblysmall inuence onthe shape: 'of =thetcurve of the current traversing the deii'ecti-ngi coil,- an--ind-uctan-ce ratiohofthe Vorder oi' magnitude of 11100 is desirable,.-softhat.in.the example referred to above the inductance .included in the parallel circuitfwill have toamount to about 170: henries. A ehokehaving-such .an inductance and-'capableof carryinga directcurrent vof about 7:0 .mill-iarnperes is veryclumsy and expensive; moreover, there .will arise other. causes -ot-distortion due tothe unavoidable natural-(distributed) capacity and lthelolfnnic resistance, also, will be considerable.

More particularly a v'nigh power cathode-ray tube, such as:projectionitubesfdoes not-permit a satisfactory:solutionvtoabe arrived vat fin the mannerset outabove.

The present invention --provides a dev-ice by means of-whichin a circuit arrangement, in which thedetiecting coils-of ar cathode-raytube are interposed in the anodecireuit of 'an lamplifying tube, to Whose grid circuit is supplied a sawtooth voltage -and inl which the anode voltage `is-suppled to :theffanode through -af circuit: connected in parallelitvith the:delectingffcoills,fasavvtoothK current is obtained in the deflecting coils by supplying, according to the invention, a correcting voltage E.; gm

with the correct phase to the grid of the amplifying tube, in which Ip represents the alternating component of current in the parallel circuit and gm the mutual conductance or transconductance of the tube.

The invention will be more fully explained by reference to the accompanying drawing, wherein Figure 1 represents one embodiment thereof.

The circuit represented in the drawing comprises an amplifying tube I having a high internal resistance, such as -for example a pentode having a cathode 2, a control grid 3 and an anode I besides the usual additional elements. A sawtcoth voltage is supplied to the input terminals 5 and 6 of the circuit. The anode circuit of the tube I comprises deflecting coils 'I which have to be fed with a sawtooth current by the tube I. The anode voltage of the tube I is supplied to the anode 4 of the tube I through a circuit which is connected in parallel with the deflecting coils 'I and comprises the series-connection of a resistance 3 and a choke 9. To prevent the direct anode current from flowing through the deflecting coils there is provided a blocking condenser I9. In parallel with the resistance 8 is connected the primary winding I I of a transformer I2 whose secondary is connected in the grid circuit of tube I in series with the input terminals 5 and 6. In accordance with the value of the resistance 3 the transformer I3 is constructed in such manner that the fundamental frequency and the harmonics of the sawtooth current entering into account are transmitted in the same ratio.

According to the invention the Values of the resistance 8 and the ratio of transformation of the transformer I2 are chosen in such manner that a correcting voltage Egg gm is supplied through the winding I2 to the control grid of the tube, in which expression Ip represents the value of the alternating component of current in the parallel circuit 8, 9 and gm the mutual conductance of the tube I. If the phase of the voltage is correctly chosen the wave form of the current through the deflecting coils 'I is perfectly equal to the sawtooth voltage applied between the terminals 5 and 6.

I claim:

1. An electric circuit arrangement comprising a discharge tube having a cathode, a control grid and an anode, means to apply a source of direct current potential to the anode, means to connect the cathode to the negative pole of said source, an inductor and a resistor connected in series with each other and in series with the positive pole of said source and said anode, a coil connected between the anode and cathode, means to apply a saw-tooth voltage between said control grid and cathode, means to derive a potential proportional to the current through said resistor, and means to superimpose in phase opposition said derived potential on the voltage applied to said control grid to produce in said coil a current variation of substantially saw-tooth wave form.

2. An electric circuit arrangement comprising a discharge tube having a cathode, a control grid and an anode, means to apply a source of direct current potential to the anode, means to connect the cathode to the negative pole of said source, an inductor and a resistor connected in series with each other and in series with the positive pole ci said source and said anode, a coil connected between the anode and cathode, means to apply a saw-tooth voltage between said control grid and cathode, means to derive a potential proportional to the current through said resistor, said potential being substantially equal to the quotient of the alternating current component of the anode current owing through said resistor divided by the mutual conductance of the tube, and means to superimpose in phase opposition said derived potential on the voltage applied to said control grid to produce in said coil a current variation of substantially saw-tooth wave form.

3. An electric circuit arrangement comprising a discharge tube having a cathode, a control grid and an anode, means to apply a source of direct current potential to the anode means to connect the cathode to the negative pole of said source, an inductor and a resistor connected in series with each other and in series with the positive pole o said source and said anode, a coil connected between the anode and cathode, means to apply a saw-tooth voltage between said control grid and cathode, means to derive a potential proportional to the current through said resistor, said superimposed potential being substantially equal to the quotient of the alternating current component of the anode current flowing through said resistor divided by the transconductance of the tube, and means comprising a transformer to superimpose in phase opposition said derived potential on the voltage applied to said control grid to produce in said coil a current variation of substantially saw-tooth wave form.

MENNO WOLF.

REFERENCES CITED The following references are of record in the of this patent:

UNITED STATES PATENTS Number Name Date 2,077,574 Maloi Apr. 20, 1937 2,085,409 Bedford June 29, 1937 2,086,918 Luck July 13, 1937 2,101,529 Tolson et al Dec. 7, 1937 2,166,688 Kell July 18, 1939 2,241,762 Blumlein May 13, 1941 2,280,733 Tolson Apr. 2l, 1942 2,284,378 Dome May 26, 1942 2,302,161 Woerner Nov. 17, 1942 2,320,551 Bahring June 1, 1943 

